1. Field of the Invention
The present invention relates to a cylinder throwing-off/throwing-on controller for effecting movement of blanket cylinders of printing units from a printing position to a non-printing position, as well as movement of the blanket cylinders from the non-printing position to the printing position, and more particularly to a cylinder throwing-off/throwing-on controller for a multicolor lithographic rotary press having a plurality of printing units for effecting multicolor printing.
2. Description of the Related Art
In a multicolor lithographic rotary press, a new paper web is spliced to a paper web currently being pulled out of a paper feed unit and is fed to printing units to thereby follow the currently fed paper web. Such a multicolor lithographic rotary press is provided with a cylinder throwing-off/throwing-on controller which throws off the cylinders of each printing unit in order to enable a spliced portion, at which the new paper web is superposed on the currently fed paper web, to smoothly pass through the printing units. A conventional cylinder throwing-off/throwing-on controller is disclosed in, for example, Japanese Patent Publication (kokoku) No. 7-381 entitled
"Cylinder Throwing-off Method for a Printing Press."In the cylinder throwing-off/throwing-on controller disclosed in Japanese Patent Publication No. 7-381, a pulse signal is generated every time a paper web moves a predetermined distance with operation of the rotary press, and a printing speed is calculated on the basis of a measured time interval between the pulse signals. A moving time of the paper web in a section of a transport path between a paper splicing position at which a paper splicing signal is generated and a position at which the paper web comes into contact with the blanket cylinder of a first printing unit is calculated on the basis of the printing speed and the length of the section along the transport path. Further, a moving time of the paper web in a section of the transport path between adjacent printing units is calculated on the basis of the printing speed and the length of the corresponding section along the transport path.
The moving times of the paper web calculated in the above-described manner are corrected for a delay in outputting a detection signal upon detection of the paper splicing position, as well as a delay in operation of a cylinder throwing-off apparatus of each printing unit, in order to calculate a time delay before outputting a cylinder throwing-off signal to each of the first through n-th printing units. In accordance with the thus-calculated delay times, cylinder throwing-off signals are sequentially output to the cylinder throwing-off apparatuses of the respective printing units.
The period of time during which the cylinder is maintained at the non-printing position is calculated on the basis of the above-described printing speed and a moving distance of a paper web between a point in time when the cylinder throwing-off operation is started and a point in time when the cylinder throwing-off operation is ended, wherein the printing speed and the moving distance are stored as preset values. The cylinder throwing-off operation at each printing unit is ended in accordance with the thus-calculated values.
The system comprises memory, an input interface, an output interface, and a CPU. The memory stores therein a calculation equation and various calculation elements such as the distance along the paper web transport path between the position at which the paper splicing signal is generated and the position at which the paper web comes into contact with the blanket cylinder of the first printing unit; the distance along the transport path between adjacent printing units; the delay in outputting a detection signal upon detection of the paper splicing position; the delay in operation of the cylinder throwing-off apparatus of each printing unit; and a distance over which the paper web passes the corresponding printing unit between a point in time when the cylinder throwing-off operation is started and a point in time when the cylinder throwing-off operation is ended. The input interface receives the pulse signals and the detection signal generated upon detection of the paper splicing position. The CPU outputs the cylinder throwing-off signal via the output interface. The CPU receives various signals via the input interface, performs calculation on the basis of the calculation equation and the calculation elements, and in accordance with the calculated values successively outputs several cylinder throwing-off signals via the output interface. (Hereinafter, the above-described prior art technique will be referred to as the "first conventional technique.")
Further, the patent publication--which discloses the first conventional technique--discloses another cylinder throwing-off/throwing-on controller. In this cylinder throwing-off/throwing-on controller, a counter is provided for each printing unit, and a pulse signal is generated every time a paper web moves a predetermined distance. In the first printing unit, upon receipt of a detection signal generated upon detection of a paper splicing position at which paper splicing is performed, the counter corresponding to the first printing unit is caused to count the pulse signal. When the counted value has reached a preset value, a cylinder throwing-off signal is output to the cylinder throwing-off mechanism of the first printing unit. At the same time, the cylinder throwing-off signal is output to the counter corresponding to the next or second printing unit as a signal which instructs start of pulse signal counting. When the counter corresponding to the second printing unit has counted a preset number of pulse signals, a cylinder throwing-off signal is output to the cylinder throwing-off mechanism of the second printing unit. This operation is repeated for the downstream printing units. In an exemplary case in which the cylinder throwing-off/throwing-on controller is used in a four-color rotary press, four counters are provided in order to sequentially throw off the cylinders of the printing units for respective colors. (Hereinafter, the above-described prior art technique will be referred to as the "second conventional technique.")
The above-exemplified conventional techniques involve the following problems.
In the first conventional technique, calculation by use of various calculation elements is performed in the CPU on the basis of the calculation equation; the result of the calculation is stored in the memory; and a cylinder throwing-off signal is output to each of the printing units via the output interface. Such accurate control requires a complicated control system, and the complexity results in a high frequency of occurrence of failures and high cost of the apparatus itself.
Further, a paper web easily stretches due to changes in printing conditions such as printing speed and paper web tension. Therefore, even when a moving time corresponding to a moving distance of the paper web is calculated accurately and the cylinder throwing-off operation is performed on the basis of the thus calculated moving time, the timing of cylinder throwing-off deviates from the timing at which the spliced portion of the paper web passes by the corresponding blanket cylinder, due to an error in the moving distance stemming from the stretch of the paper web, resulting in a possibility that printing cannot be performed stably.
In the second conventional technique, since the counter for counting reference signal pulses is provided for each printing unit, counters equal in number to the printing units are required, so that the number of parts increases, resulting in increased cost. Further, maintenance is cumbersome.
The printing units of a multicolor lithographic rotary press are disposed such that the distance between adjacent printing units is reduced to a greatest possible extent, in order to perform multicolor printing in a more stable manner. In addition, recently, the printing operation has been performed at extremely high speed, and therefore, the time which each portion of a paper web requires to pass through a section between adjacent printing units is very short. Moreover, a period of time longer than an operation delay of the cylinder throwing-off apparatus is required for completing the cylinder throwing-off operation after issuance of the corresponding cylinder throwing-off signal.
As described above, in the second conventional technique, a counter is provided for each printing unit; simultaneously with completion of the counting operation of the counter of the first printing unit, a cylinder throwing-off signal is output to the counter corresponding to the second printing unit; and such signal input and output is repeated from the second printing unit to the final printing unit in order to perform cylinder throwing-off operation. Therefore, there is a possibility that the spliced portion of paper web passes through the contact portion at which the paper web comes into contact with the blanket cylinder before completion of the cylinder throwing-off operation started in response to the output signal of the corresponding counter. Accordingly, multicolor printing cannot be performed in a stable manner.